The present invention relates to an apparatus and a method for welding joint fixtures such as flanges and elbows at either end of a pipe. More particularly, it relates to an apparatus and a method for automatically welding joint fixtures at either end of a pipe at predetermined angles.
In the manufacturing of steel pipes for hydraulic pipings of power machines used in various industries and construction works such as bulldozers and power shovels, joint fixtures such as flanges and elbows are attached to either end of a pipe to connect the same with relevant parts within the machine. Joint fixtures such as elbows do not always open in the same direction at both ends of a pipe; rather, they are often welded at different angles so that the pipe ends on both sides would open in different directions from each other. Pipe products of this type are in most cases formed with one or more bent portions 91 as shown in FIG. 14. These bends 91 are formed after joint fixtures 92a, 92b are welded to a straight pipe 90. Thus, each joint fixture is welded to a pipe end at an angle which is determined based on the anticipated final pipe configuration with bends.
As one prior art means for welding joint fixtures to either end of a pipe at predetermined angles, there is known a method which utilizes a jig that in turn includes a plate and blocks provided on either side of said plate to support the joint fixtures at predetermined angles.
According to the prior method, each joint fixture is placed on respective blocks so that each can be held and fixed at predetermined angles. Thus held at predetermined angles, each joint fixture is tentatively welded to a pipe end by welding at several spots on the periphery. The pipe attached with the fixtures is then detached from the jig, and the junctions between the pipe ends and the fixtures are firmly connected by welding while rotating the pipe assembly.
The prior art method mentioned above is defective in that a jig must be fabricated each time to accommodate to specific requirements such as the configuration, size and the angle of attachment of the fixtures. This involves considerable time, labor and cost even before proceeding with the welding operation. It also requires a large space and cost to store and adequately maintain the jigs of different specifications for future use. Use of the jig is further defective in that the flow in the welding operation is disturbed when the pipe tentatively fixed with the joint fixtures is detached from the jig and transferred to a welding apparatus for final welding. This adversely affects operationally efficiency and results in a higher production cost.